Abstract
The coccinellid Harmonia axyridis is a recent arrival in the UK and is an intraguild predator of the entomopathogenic fungus Pandora neoaphidis. Harmonia axyridis entirely consumes P. neoaphidis-sporulating cadavers and this may have a negative effect on the epizootic potential of P. neoaphidis. Here we assessed within plant transmission, and between plant vectoring, of P. neoaphidis in the presence of either H. axyridis or Coccinella septempunctata, a native coccinellid that only partially consumes fungal cadavers. Transmission was greater in the presence of coccinellids, with 21% of aphids becoming infected with the fungus whilst only 4% were infected in the control. However, there was no significant effect of coccinellid species or sex on fungal transmission. Between plant vectoring occurred infrequently in the presence of both species of coccinellid. The effect of H. axyridis on P. neoaphidis transmission is, therefore, likely to be similar to that of the native coccinellid C. septempunctata.
Highlights
Aphid populations are regulated by predators, pathogens and parasitoids
There was no difference in the proportion of aphids eaten by H. axyridis in the presence or absence of P. neoaphidis (F2 = 1.08, df = 1, p = 0.345) or by male and female H. axyridis (F2 = 1.68, df = 1, p = 0.20) (Table 1)
Transmission in the presence of H. axyridis and C. septempunctata was not significantly different (F1,41 = 0, p = 0.997) with a mean of 22% and 21% P. neoaphidisinfected aphids recovered in the presence of H. axyridis and C. septempunctata respectively (Fig. 1)
Summary
Aphid populations are regulated by predators, pathogens and parasitoids. Interactions between aphid enemies may have positive, neutral or negative effects on pest control (Rosenheim et al, 1995; Ferguson & Stiling, 1996; Straub et al, 2008). The presence of foraging native predators, parasitoids and extraguild co-occurring arthropods all increase local transmission of P. neoaphidis by increasing aphid movement and, the encounter rate with infective conidia (Pell et al, 1997; Feuntes-Contreras et al, 1998; Roy et al, 1998, 2001; Baverstock et al, 2008). (Coleoptera: Coccinellidae) vectors P. neoaphidis to previously uninfected aphid colonies on different plants, thereby enhancing dispersal (Roy et al, 2001).
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